This invention relates to analog to digital conversion in general and more particularly to an improved method and a circuit arrangement for converting an analog quantity into a digital quantity, in which the analog quantity is fed to an integrating circuit, to which a reference quantity is temporarily connected during a conversion period and in which the pulses delivered by a pulse generator are also fed to a counter during the time when the reference quantity is connected to the integrating circuit.
A method of the general type is disclosed in German Auslegeschrift No. 1 295 628. It is a disadvantage in this known method that the integration circuit is reset prior to the start of each conversion period by shorting the output to the input and that the analog quantity is disconnected during the resetting time. A change of the analog quantity occurring during this resetting time will therefore be missed and the result of the conversion is accordingly inaccurate.
The same is also true for the known dual slope method of conversion. In this method, the analog quantity is integrated over a given period of time, is then disconnected from the integrator and the reference quantity is connected for integrating down the output signal of the integrator. In this known method, the analog quantity is not sensed during the time that the reference quantity is connected to the integrator.
German Offenlegungsschrift No. 24 39 475 describes a method for converting an analog quantity into a digital quantity, in which the analog quantity is sensed continuously. It is a disadvantage of this method, however, that no constant duration for the converted average value is obtained in the conversion of an analog quantity into a digital quantity. In this known method, one obtains greatly different values for the individual conversion period, so that an average value must again be formed from a multiplicity of conversion periods.